Positive displacement pumps, such as piston or plunger pumps are typically employed for high pressure applications, such as abrasive cutting and hydraulic fracturing operations. Such pumps are sometimes called triplex or positive displacement pumps. Plunger pumps typically include one or more plungers driven by a crankshaft toward and away from a chamber in a pressure housing (typically referred to as a “fluid end”) in order to create pressure oscillations of high and low pressures in the chamber. These pressure oscillations allow the pump to receive a fluid at a low pressure and discharge it at high pressure through suction and discharge check valves. The suction and discharge check valves, open and close in conjunction with the fluid displacement of the pump plunger or piston, which in turn controls the flow of fluids through the pump.
Note that pumping particle fluids through a piston or plunger pump requires extensive maintenance and replacement of the check valves and plungers due to the nature of abrasive material eroding the pump parts making the overall pump life expectancy low.
Accordingly in many applications to protect the plunger pump from extreme wear while pumping abrasive materials, a less particle fluid is pumped through the plunger pump downstream to be mixed externally with an abrasive material stored in an abrasive pressure vessel as described in Judge et al., U.S. Pat. No. 6,904,982. The abrasive vessel has to withstand the high pressure of the plunger pump and requires the abrasive to be loaded without pressure, thus only the one batch of abrasive contained in the pressure vessel is available to be blended with the high pressure plunger pump fluid.
A problem that may exist in slurry pumps is that when the pump is stopped, the solid particles fall out of the carrier fluid. Cleaning out such solid particles from the pump before the pump may be restarted, takes the pump out of service a considerable amount of time.
Multiple plunger pumps are often employed simultaneously in large scale hydraulic fracturing operations with perhaps as many as thirty plunger pumps coupled together through a common manifold with each plunger pump having its own pressurized storage vessel.
A high pressure slurry plunger pump is disclosed by Oglesby, U.S. Pat. No. 7,794,215 wherein a high pressure piston style pump is used to pressurize a slurry material. The patent purports to create a clean fluid buffer that removes slurry from around the suction and discharge valves.
Purportedly, to “clean” the suction valve, before the piston is fully retracted, clean water is injected into the reservoir before the suction valve. In theory as the piston continues to reverse, the “clean” water is drawn through the suction valve such that when the piston is fully retracted the seating area of the suction valve is free of abrasive material. Similarly, to “clean” the discharge valve, as the piston nears full retraction, clean water is injected in front of the piston. At least in theory, as the piston completes its forward cycle, the injected clean water in front of the piston is the last to exit through the discharge valve thereby making the seating area of the discharge valve free of abrasive material. Besides the inherent difficulty of timing the clean water injections perfectly, there is an inherent problem with this solution. The clean water is allowed to mix with the slurry; therefore, it is almost impossible for the valves seating areas to truly be clear of abrasives (e.g. there will still be abrasive in the valve seating area). Therefore, what is needed is a solution which actually clears the valve seating areas of abrasives.
Abrasive cutting using a high pressure pump is described by McAfee U.S. Pat. No. 7,527,092 that requires batch storage of abrasive in a pressure vessel. High pressure abrasive vessels require frequent government code re-certification and are costly to purchase. Therefore, what is needed is a solution which allows abrasive to be pumped directly through a plunger pump at high pressure and does not require a costly pressure vessel.
Additionally, with all of the preceding, and other solutions available, it is difficult and costly to pump particles at high pressure, such as steel shot, formation propping material, or abrasive material, directly through a plunger or piston pump without damaging or destroying the pump.